ABSTRACT
A creep force model that predicts the effects of water on adhesion in the wheel-rail contact depending on the water rate is presented. The focus is laid on the consideration of boundary lubrication phenomena occurring when low amounts of water get into the contact. The developed WILAC model (Water Induced Low Adhesion Creep force model) represents a computationally efficient engineering tool based on Polach’s creep force model with contact normal force and vehicle speed dependent parameters. The water rate represents a direct model input quantity. Results from tribological and full-scale testing under wet conditions have been used for model parameterization. Adhesion values as low as ca. 0.05 were observed at high creepage with only wear debris and little water present in the contact. The so called ECF model (Extended Creep Force model) has been used to parameterize the dependency of the creep force with respect to contact normal load and rolling speed. The WILAC model will improve the prediction quality of vehicle-dynamics, traction and braking simulations, etc. Furthermore, the model can be used e.g. for the detection of weather related low adhesion conditions and the mitigation of correlating safety issues (station overruns, signal passing at danger, etc.).
